Solid tissue cancers start to grow at a primary site. As the disease progresses, metastases arise at distant locations. These metastatic events accelerate the disease and eventually lead to death. Cells or fragments of cells leave the primary site as part of the metastatic process. The process of metastasis is complex. Part of the metastatic process involves rare circulating tumor cells (CTC). That these CTC are not a monolithic population within a given patient is becoming clear. Fractionation of the CTC's within a patient is essential to understand the mutations responsible for the cancer afflicting the patient. Purification and isolation of these rare tumor cells (or cell derived events) is required to define oncogenic mutations in patient blood. Many cells and cell fragments exist in whole blood that do not contain mutations, thus in order to isolate the useful mutation bearing cells, a purification strategy is required.
In order to measure mutations in the DNA genome of a rare cell population, e.g., circulating tumor cells (CTC), from a mixture of cells, by any technology, DNA of sufficient quantity and quality is required. Typically from 2 to 4 ml of whole blood, one can expect 2 to 10 CTCs to be recovered. This number of cells must be processed with excellent recovery to ensure that mutation bearing chromosomes are not lost during processing.